In recent years, various functionalities such as radio frequency identifications (RFIDs), near field communications (NFCs), wireless chargers, or pen tablets have been added in portable terminal devices such as smart phones, tablet personal computers (PCs), or notebooks. Since most of the various functionalities added in the portable terminal devices use the magnetic fields, magnetic fields of 100 kHz˜several tens of MHz are generated. The magnetic field generated from the portable terminal device will affect various components such as a battery incorporated in the mobile terminal device.
Thus, it is necessary to use a magnetic field shielding sheet in a portable terminal device, in order to prevent components such as a battery of the portable terminal device from being influenced due to a magnetic field generated from the portable terminal device, and in order to improve an ability of using the magnetic field by focusing the magnetic field.
An electromagnetic wave shielding member using a conventional ribbon, as disclosed in Korean Patent Publication No. 10-0460297 (on Nov. 26, 2004), includes: a metal ribbon composed of any one metal or alloy selected from the group consisting of Ni—Fe—Mo, Fe—Si and mu-metal and whose relative magnetic permeability is 1000 or more, in which the thickness of the metal ribbon is between 1 μm and 900 μm, and the width of the metal ribbon is in the range of from 1 mm to 90 mm; and an adhesive layer formed on at least one side of the metal ribbon.
Such a conventional electromagnetic wave shielding member may cause radiation to the opposite side of the metal ribbon which a magnetic field enters, in which the magnetic field passes through and along the plane of the metal ribbon when the magnetic field is applied from outside along the side of the metal ribbon in the case that the metal ribbon is in a flat plate form. As a result, a geomagnetic sensor which employs the conventional electromagnetic wave shielding member may cause a sensitivity strength difference in the X-, Y-, and/or Z-direction, to thereby cause a problem that an angular error occurs.
Then, in the case that the metal ribbon is flake-processed to then be divided into a plurality of flakes or to then be formed into cracks, even if a magnetic field is applied from the outside along one side of the metal ribbon, the magnetic field is attenuated while passing through the flakes or cracks, and thus the magnetic field does not nearly radiate to the opposite side of a magnetic field shielding sheet which the magnetic field enters.
However, in the case of flake-processing a Fe-based metal ribbon, moisture may penetrate into the gap between the flakes or cracks of the metal ribbon to thereby cause a problem that the metal ribbon is easily oxidized.
Thus, as described above, when the metal ribbon is oxidized, a problem in appearance is generated, and the characteristics of elements combined with oxygen may be changed to thus cause a problem that the shielding property decreases.